(1) Field of the Invention
The present invention relates to the heating of fluids and particularly to the heating of water for domestic purposes with the aid of solar energy. More specifically, this invention is directed to solar assisted hot water heating systems and to heat exchangers for use therein. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is believed to be particularly well suited for use in the preheating of cold water prior to its delivery to a domestic hot water heater or in the supplementary heating of fluid within the tank of a hot water heater. The hot water heating systems presently in use include separate heating tanks equipped either with one or more electric heating elements or a burner which is fired with a hydrocarbon fuel. There are, additionally, so called "domestic" hot water heating systems which include a heat exchanger integral with a boiler employed to produce hot water or steam for residential heating purposes. In all hot water heating systems previously commerically available, cold water, for example from the city supply, was delivered directly to the heating apparatus and the sole source of thermal energy for heating the water was derived, either directly or indirectly, from the combustion of a hydrocarbon fuel.
Because of rapidly escalating energy costs, it has been proposed to reduce energy consumption needed for the production of hot water for domestic purposes by means of preheating the water prior to its delivery to the hot water heater. Numerous preheating schemes, in various degrees of complexity and practicality, have been proposed. These preheating schemes may be classified as either those which seek to recover thermal energy which would otherwise be wasted, for example through installation of some form of heat exchanger in the exhaust stack from the building heating furnance, and those which collect and employ solar energy. The waste heat recovery schemes proposed to date have been characterized by complexity, difficulty in installation and their reliability has been suspect. The preheating schemes based upon the use of solar energy have included the generation of electrical energy for use in energizing heating elements, for example through the use of windmills or solar cells, or have utilized solar energy for the purposes of directly heating fluid. Because of the notorious inability to store electrical power, the proposed preheating schemes based upon the generation of electrical energy for delivery to an electric heating element have proved to be impractical. Previously proposed schemes for using solar energy to directly heat a fluid have been characterized by a number of inherent deficiencies. These deficiencies include poor efficiency, which has made the necessary investment in capital equipment unattractive, and complex control schemes which have significantly increased the cost of the equipment which must be acquired.